In light source devices for liquid crystal projectors and DLP projectors which are required to be reduced in size and can provide bright projection images, short arc type high pressure mercury vapor discharge lamps which are small in size and can provide light emission at high brightness have been used and, since the lamps of this type involve a problem that starting performance under cold condition and restarting performance under hot restrike condition is not generally preferred, start assisting light sources are provided to enhance the starting performance.
An existent light source device shown in FIG. 7 includes: a high pressure discharge lamp 51 of short arc type in which a discharge chamber 54 having a pair of tungsten electrodes 56, 56 opposed each other at a short inter-electrode distance of about 1 mm and mercury, halogen, e.g., bromine and a starting gas such as an argon gas filled therein is formed in the center of an arc tube 52 formed of a quartz glass tube, a pair of electrode seal portions 59R, 59L each having the electrode 56, a metal foil 57, and an electrode lead 58 sealed therein are formed from the discharge chamber 54 to both ends of the arc tube 52, and connected to a lighting circuit by way of the electrode leads 58, 58 protruding from the end faces of the electrode seal portions 59R, 59L, a concave reflector 61 to which the electrode seal portion 59L on one side of the lamp 51 is secured by being inserted through a bottom hole 62 opened in the bottom of the reflector, and an ignition antenna 63 as a start assisting light source that radiates UV-light to the discharge chamber 54 for enhancing the starting performance of the lamp 51 upon startup lighting thereof (refer to Patent document 1).
As shown in an enlarged view of FIG. 8(a) and in a cross sectional view along X-X of FIG. 8(b), the ignition antenna 63 has an antenna vessel 64 formed of a quartz glass tube comprising a long straight tube portion 65a that extends as far as the proximity of the discharge chamber 54 of the lamp 51 along the electrode seal portion 59L and a bent tube portion 65b that is provided to the top end of the tube portion 65a and bent in a semi-arcuate shape so as to be wound by 180° around the outer periphery of the electrode seal portion 59L. Mercury and an argon gas as ionizing filler are filled in the vessel, an electric conductor element 66 comprising a metal foil (molybdenum foil) is contained and disposed on the side of the free end of the straight tube portion 65a of the antenna vessel 64, and an outer electrode 67 comprising a metal bush is fitted on the side of the free end of the straight tube portion 65a. 
Then, the ignition antenna 63 is secured at the outer electrode 67 to the outer periphery of the electrode seal portion 59L with cement 68, the outer electrode 67 is connected by way of a current supply conductor 69 to the output of voltage transforming means 71 connected between current conductors 70R, 70L that constitute the lighting circuit of the high pressure discharge lamp 51. When a starting voltage such as a high frequency AC voltage or pulse voltage is applied between the outer electrode 67 and the electric conductor element 66 in the antenna vessel 64, electric discharge is caused between them to generate UV-light, and the UV-light is radiated through the straight tube portion 65a and the bent tube portion 65b into the discharge chamber 54 of the lamp 51 thereby promoting arc discharge between the electrodes 56 and 56.
However, it is laborious to manufacture the antenna vessel 64 comprising the straight tube portion 65a and the bent tube portion 65b contiguous to each other and this results in a drawback of increasing the manufacturing cost. Further, since the bent tube portion 65b of the antenna vessel 64 is in proximity to the discharge chamber 54 of the lamp 51 which is heated to a high temperature of about 1000° C. upon lighting of the lamp, this results in a problem that discharge between the outer electrode 67 and the electric conductor element 66 is instable due to the effect of the high temperature just after turning off the lamp to deteriorate the restarting performance under hot conditions and, at the same time, the antenna vessel 64 may be possibly fractured while undergoing thermal damages.
Further, there is also a disadvantage that UV-light generated by the electric discharge between the outer electrode 67 and the electric conductor element 66 is attenuated by reflection, diffraction, or absorption to the filler in the antenna vessel 64 in a process where the UV-light is guided through the long straight tube portion 65a and the bent tube portion 65b of the antenna vessel 64 to the inside of the discharge chamber 54 of the lamp 51. Further, since the bent tube portion 65b of the antenna vessel 64 is disposed in proximity to one side of the discharge chamber 54 of the lamp 51, the temperature distribution during lighting of the lamp is significantly different between one side and the other side of the discharge chamber 54, to possibly deteriorate the lamp working life. At the same time, it also results in a disadvantage that the bent tube portion 65b of the antenna vessel 64 interrupts a portion of light radiated from the discharge chamber 54 of the lamp 51 to the bottom of the concave reflector 61, thereby lowering the efficiency of utilizing the light of the lamp. Further, there may be also a possibility that the ignition antenna 63 is detached from the outer periphery of the electrode seal portion 59L due to aging deterioration (thermal deterioration) of the cement 68 that secures the ignition antenna 63 to the electrode seal portion 59L.
Then, the present applicant proposed a light source device as shown in FIG. 9 in which a glow discharge tube 80 that generates UV-light upon startup lighting of the high pressure discharge lamp 51 is disposed at a position capable of radiating UV-light to the discharge chamber 54 of the lamp 51 from the outside of a concave reflector 81 through a vent hole 82 for cooling air formed in the reflector (refer to Patent Document 2).
In the light source device in FIG. 9, since the high pressure discharge lamp 51 having a basic structure identical with that of the high pressure discharge lamp in FIG. 7 is inserted at an electrode seal portion 59L on one side thereof through a bottom hole 83 opened in the bottom of a reflector 81 and mounted integrally to the reflector 81, and a glow discharge lamp 80 as a start assisting light source radiates UV-light for enhancing the starting performance to the discharge chamber 54 upon startup lighting of the lamp 51 is disposed outside of the reflector 81, the mercury vapor pressure inside the discharge tube 80 is not increased excessively even when heated to a high temperature upon lighting of lamp and can cause glow discharge to generate UV-light also under hot conditions just after turning off of lamp.
Further, since the glow discharge tube 80 has a simple structure of sealing a rare gas such as an argon gas containing mercury vapor inside a glass seal tube 84 comprising quartz glass, containing and disposing an inner electrode 85 comprising a metal foil and having a pair of lead wires 86, 86 that protrude from both ends of the glass seal tube 84 and disposing a coiled outer electrode 87 formed by winding a chromium-aluminum iron alloy wire 89 having a diameter of about 0.2 mm around the outer periphery of the glass seal tube 84, it has an advantage that the manufacturing cost is not increased.
The inner electrode 85 and the outer electrode 87 of the glow discharge tube 80 are connected to one side 88R and the other side 88L of a lamp lighting circuit respectively. When a starting high frequency pulse voltage is applied between the inner electrode 85 and the outer electrode 87, glow discharge is caused in the mercury vapor in the glass seal tube 84 as a main body of the discharge tube 80 to generate UV-light, and a portion of the UV-light is radiated directly through the vent hole 82 for cooling air formed in the reflector 81 to the discharge chamber 54 of the lamp 51 disposed inside the reflector 81, or radiated after being reflected at the reflection surface of the reflector 81.
However, when the discharge tube 80 is disposed at a position remote from the vent hole 82 of the reflector 81, the amount of UV-light radiated through the vent hole 82 to the inside of the reflector 81 is decreased to result in a problem of lowering the starting performance of the lamp 51. On the other hand, when the discharge tube 80 is disposed in proximity to the vent hole 82 of the reflector 81, since the vent hole 82 is closed by the discharge tube 80, the flow of the cooling air is hindered to result in a problem of lowering the cooling effect for the lamp 51.
Further, there is also a problem that when the number of turns of the coils of the coiled outer electrode 87 disposed to the outer periphery thereof is insufficient, since the generation amount of UV-light is small, the discharge tube 80 cannot radiate the UV-light in a necessary and sufficient amount to the discharge chamber 54 of the lamp 51. On the other hand, when the number of turns of the coils of the coiled outer electrode 87 is increased, UV-light is interrupted by the outer electrode 87 to result in a problem that the UV-light cannot be radiated in a necessary and sufficient amount to the discharge chamber 54 of the lamp 51.
Then, a high pressure discharge lamp 91 shown in FIG. 10(a) is different in view of the type and the structure from the high pressure discharge lamp 51 described above. A discharge chamber 92 and a UV enhancer 93 as a start assisting light source that radiate UV-light to the discharge chamber are contained inside an outer chamber 95 having a lamp cap (base) 94 (refer to Patent Document 3).
In the discharge chamber 92, a pair of opposed inner electrodes 96L and 96R in the inside thereof are connected by way of power feeder wires 97, 98 to one contact and the other contact of a lamp cap 94 by way of power feeder wires 97, 98 respectively.
As shown in the cross sectional view of FIG. 10(b), in the UV enhancer 93, a rare gas comprising an argon gas is filled inside a UV-discharge tube 99 having a tube wall formed of a ceramic material comprising sintered polycrystal Al2O3, and an inner electrode 101 comprising a tungsten rod having a 170 μm diameter welded to the top end of a lead through conductor 100 comprising a niobium rod having a 620 μm diameter sealed on one side of the UV-discharge tube 99 is disposed. Then, the inner electrode 101 is connected by way of the lead through conductor 100 to the power feeder wire 97, and the UV-discharge tube 99 is disposed being supported by the lead through conductor 100 in the proximity to the power feeder wire 98, and capacitively coupled with the power feeder wire 98 to act as a UV-source.
However, the high pressure discharge lamp 91 in FIG. 10(a) has a drawback that the UV-enhancer 93 as the start assisting light source interrupts the light radiated from the discharge chamber 92 to lower the light use efficiency, or causes unevenness in the brightness or shadow. Further, since the UV-enhancer 93 has a configuration of supporting one end of the UV-discharge tube 99 comprising the ceramic material by the lead through conductor 100, when an impact exerts from the outside to the high pressure discharge lamp 91, the UV-discharge tube 99 swings greatly by the impact and the lead through conductor 100 is deformed by dynamic load of the discharge tube 99 thereby causing positional displacement of the discharge tube 99 to deteriorate capacitive coupling with the power feeder wire 98 to no more function as the UV-source, or the lead through conductor 100 connected to the power feeder wire 97 may be possibly in contact with the other power feeder wire 98 to result in short circuit accident.